库车坳陷盐相关构造与有利油气勘探领域

SALT-RELATED STRUCTURES AND FAVORABLE HYDROCARBON TRAPS IN THE KUQA DEPRESSION

野外露头、钻井和地震资料证实,库车坳陷古近系库姆格列木组(西部)和新近系吉迪克组(东部)沉积有较厚的膏盐层。在浮力、重力、沉积差异负载和挤压应力等因素综合作用下,盐体发生明显的塑性流动,围绕拜城凹陷呈环带状分布,并在克拉苏构造带和秋里塔格构造带聚集增厚,最厚可达4000m以上。盐体的塑性变形影响了含盐层系和上覆层的构造变形过程,形成了数量众多、类型丰富的盐相关构造,主要包括盐枕、盐墙、盐推覆、鱼尾、盐焊接(断层焊接)、盐垛、突发构造和盐撤凹陷等。库车坳陷盐相关构造变形影响了油气运移、聚集和成藏过程。盐构造运动形成的丰富圈闭可为油气聚集提供良好的空间,断裂可为油气运移提供良好通道,巨厚的膏盐层还可作为封闭性能良好的盖层。受盐相关构造变形影响,库车坳陷盐下、盐间和盐上存在三种不同的成藏模式。综合分析表明,库车坳陷较为有利的油气勘探领域主要包括有盐下的背斜圈闭、断层遮挡下盘圈闭、地层-岩性圈闭、盐间的构造-地层圈闭和盐上的背斜圈闭等。

Comprehensive data from field observations, drilling wells and seismic profiles have demonstrated that the Paleogene Kumugeliemu Fm. and Neogene Jidike Fm. attain thick halite layers in the Kuqa depression of the northern Tarim basin, NW China. Driven by the buoyancy, gravity spreading, differential loading and compressional stresses, the salt bodies experienced viscous flowage, resulting in spatial distribution features for the circumBaicheng sag and thickening in the Kelasu and Qiulitage structural belts with the maximum thickness of 4000m. The viscous flow of salt sequences influenced the structural distortion of the halite layers and overburden. Conse- quently, many salt-related structures, such as salt pillows, salt walls, salt nappes, fish-tails, salt welds （ fault welds） , salt stacks, pop-ups and salt-withdrawal sags, have developed well in the Kuqa depression. The salt-related structures had exerted important influence on the hydrocarbon migration and accumulations. The structural and subtle traps induced by the salt structures offered abundant favorable space for hydrocarbon accumulation, the faults acted as the favorable pathways for hydrocarbon migration and the thick halite layers served as good regional seals for hydrocarbon preservation. The forming models of hydrocarbon accumulation are different in the sub-salt, salt and supra-salt in the Kuqa depression. The integrated analysis shows that the favorable exploration objectives include the sub-salt anticlinal traps, footwall fault traps sealed by reverse faults, stratigraphic-lithologic traps, midsalt structural-stratigraphic traps and supra-salt anticlinal traps.